Repeated invasions shape NZ's bird life

Since the Ice Age drastically changed the Aotearoa landscape from widely forested to grass and shrubland, researchers set out to determine which of our living and recently extinct birds are a result of existing lineages that adapted to their environment tens of millions of years ago and which are the descendants of comparatively recent invaders.

Using mitogenome data from nearly all living and recently extinct New Zealand mainland bird species, researchers discovered many species associated with grass and shrubland, like pīhoihoi New Zealand pipit and pūtangitangi paradise shelduck, colonised Aotearoa at the start of the Ice Age, most likely from Australia.

Lead author Dr Pascale Lubbe, of the Department of Zoology, says despite this, suggestions that such recent immigrants are not "iconically New Zealand" are misleading.

"Repeated invasions by species are actually very typical of New Zealand's biological heritage throughout geological history," Dr Lubbe says.

"Many of our most iconic endemic birds that are found nowhere else on earth, like the Haast's eagle, kakī/black silt and fantails, are Ice Age arrivals."

Published in the international journal Molecular Ecology, researchers investigated the relationships between the birds of Aotearoa and their overseas relatives, and when they split into distinct species.

While the country's flora and fauna has been researched intensely for more than a century, previous studies have mostly been conducted on a species-by-species basis.

"Our research approach is a broad scope investigation of the global origins of nearly all our endemic bird species, providing an overall view of the evolution of these birds," she says.

"We have been able to show that colonisation patterns are driven in part by the habitat preferences of the invading species over geological time."

In today's warming world, understanding these past evolutionary changes is imperative to making sense of the rapidly changing present and increasingly uncertain future.

"With much of New Zealand's forests cleared for agriculture, many Australian bird species have established themselves here over the past century, such as welcome swallows, silvereyes, plovers and Australian coots."

Dr Lubbe says this is likely to continue.

"We must expect more Australian species to make a new home on our shores as time goes on, with consequent biosecurity risks, especially if New Zealand continues to lose forest cover.

"Doubly so if our endemic species go extinct, leaving their ecological roles empty."